Firewall configuration

The firewall configuration located in /etc/config/firewall.

Overview

OpenWrt relies on netfilter for packet filtering, NAT and mangling. The UCI Firewall provides a configuration interface that abstracts from the iptables system to provide a simplified configuration model that is fit for most regular purposes while enabling the user to supply needed iptables rules on his own when needed.

UCI Firewall maps two or more Interfaces together into Zones that are used to describe default rules for a given interface, forwarding rules between interfaces, and extra rules that are not covered by the first two. In the config file, default rules come first but they are the last to take effect. The netfilter system is a chained processing filter where packets pass through various rules. The first rule that matches is executed, often leading to another rule-chain until a packet hits either ACCEPT or DROP/REJECT. Such an outcome is final, therefore the default rules take effect last, and the most specific rule takes effect first. Zones are also used to configure masquerading also known as NAT (network-address-translation) as well as port forwarding rules, which are more generally known as redirects.

Zones must always be mapped onto one or more Interfaces which ultimately map onto physical devices; therefore zones cannot be used to specify networks (subnets), and the generated iptables rules operate on interfaces exclusively. The difference is that interfaces can be used to reach destinations not part of their own subnet, when their subnet contains another gateway. Usually however, forwarding is done between lan and wan interfaces, with the router serving as 'edge' gateway to the internet. The default configuration of UCI Firewall provides for such a common setup.

Requirements

Sections

Below is an overview of the section types that may be defined in the firewall configuration.
A minimal firewall configuration for a router usually consists of one defaults section, at least two zones (lan and wan) and one forwarding to allow traffic from lan to wan. (The forwarding section is not strictly required when there are no more than two zones as the rule can then be set as the 'global default' for that zone.)

Defaults

The defaults section declares global firewall settings which do not belong to specific zones.
The following options are defined within this section:

Zones

A zone section groups one or more interfaces and serves as a source or destination for forwardings, rules and redirects. Masquerading (NAT) of outgoing traffic is controlled on a per-zone basis. Note that masquerading is defined on the outgoing interface.

INPUT rules for a zone describe what happens to traffic trying to reach the router itself through that interface.

OUTPUT rules for a zone describe what happens to traffic originating from the router itself going through that interface.

FORWARD rules for a zone describe what happens to traffic coming from that zone and passing to another zone.

The options below are defined within zone sections:

Name

Type

Required

Default

Description

name

zone name

yes

(none)

Unique zone name

network

list

no

(none)

List of interfaces attached to this zone. If omitted and neither extra* options, subnets or devices are given, the value of name is used by default. Use list syntax as explained in uci.

masq

boolean

no

0

Specifies whether outgoing zone traffic should be masqueraded - this is typically enabled on the wan zone

masq_src

list of subnets

no

0.0.0.0/0

Limit masquerading to the given source subnets. Negation is possible by prefixing the subnet with !; multiple subnets are allowed.

masq_dest

list of subnets

no

0.0.0.0/0

Limit masquerading to the given destination subnets. Negation is possible by prefixing the subnet with !; multiple subnets are allowed.

List of raw network device names attached to this zone, e.g. ppp+ to match any PPP interface. Only supported by the Firewall v2, version 58 and above ; not supported by 12.09 default installation

subnet

list

no

(none)

List of IP subnets attached to this zone. Only supported by the Firewall v2, version 58 and above, not supported by 12.09 default installation

extra

string

no

(none)

Extra arguments passed directly to iptables. Note that these options are passed to both source and destination classification rules, therfore direction-specific options like –dport should not be used here - in this case the extra_src and extra_dest options should be used instead. Only supported by the Firewall v2, version 58 and above, not supported by 12.09 default installation

extra_src

string

no

Value of extra

Extra arguments passed directly to iptables for source classification rules. Only supported by the Firewall v2, version 58 and above, not supported by 12.09 default installation

extra_dest

string

no

Value of extra

Extra arguments passed directly to iptables for destination classification rules. Only supported by the Firewall v2, version 58 and above, not supported by 12.09 default installation

Forwardings

The forwarding sections control the traffic flow between zones and may enable MSS clamping for specific directions. Only one direction is covered by a forwarding rule. To allow bidirectional traffic flows between two zones, two forwardings are required, with src and dest reversed in each.

Below is a listing of allowed option within forwardings:

Name

Type

Required

Default

Description

src

zone name

yes

(none)

Specifies the traffic source zone. Must refer to one of the defined zone names

dest

zone name

yes

(none)

Specifies the traffic destination zone. Must refer to one of the defined zone names

mtu_fix

boolean

no

0

Enable MSS clamping for traffic flowing from the source zone to the destination zone (Deprecated and moved to zone sections in 8.09.2+)

family

string

no

any

Protocol family (ipv4, ipv6 or any) to generate iptables rules for.

The iptables rules generated for this section rely on the state match which needs connection tracking to work.
At least one of the src or dest zones needs to have connection tracking enabled through either the masq or the conntrack option.

Redirects

Port forwardings (DNAT) are defined by redirect sections. All incoming traffic on the specified source zone which matches the given rules will be directed to the specified internal host.

Redirects are also commonly known as "port forwarding", and "virtual servers".

Port ranges are specified as start:stop, for instance 6666:6670. This is similar to the iptables syntax.

The options below are valid for redirects:

Name

Type

Required

Default

Description

src

zone name

yes for DNAT target

(none)

Specifies the traffic source zone. Must refer to one of the defined zone names. For typical port forwards this usually is wan

src_ip

ip address

no

(none)

Match incoming traffic from the specified source ip address

src_dip

ip address

yes for SNAT target

(none)

For DNAT, match incoming traffic directed at the given destination ip address. For SNAT rewrite the source address to the given address.

src_mac

mac address

no

(none)

Match incoming traffic from the specified mac address

src_port

port or range

no

(none)

Match incoming traffic originating from the given source port or port range on the client host

src_dport

port or range

no

(none)

For DNAT, match incoming traffic directed at the given destination port or port range on this host. For SNAT rewrite the source ports to the given value.

proto

protocol name or number

yes

tcpudp

Match incoming traffic using the given protocol

dest

zone name

yes for SNAT target

(none)

Specifies the traffic destination zone. Must refer to one of the defined zone names. For DNAT target on Attitude Adjustment, NAT reflection works only if this is equal to lan.

dest_ip

ip address

yes for DNAT target

(none)

For DNAT, redirect matched incoming traffic to the specified internal host. For SNAT, match traffic directed at the given address.

dest_port

port or range

no

(none)

For DNAT, redirect matched incoming traffic to the given port on the internal host. For SNAT, match traffic directed at the given ports.

ipset

string

no

(none)

If specified, match traffic against the given ipset. The match can be inverted by prefixing the value with an exclamation mark

mark

string

no

(none)

If specified, match traffic against the given firewall mark, e.g. 0xFF to match mark 255 or 0x0/0x1 to match any even mark value. The match can be inverted by prefixing the value with an exclamation mark, e.g. !0x10 to match all but mark #16.

start_date

date (yyyy-mm-dd)

no

(always)

If specifed, only match traffic after the given date (inclusive).

stop_date

date (yyyy-mm-dd)

no

(always)

If specified, only match traffic before the given date (inclusive).

start_time

time (hh:mm:ss)

no

(always)

If specified, only match traffic after the given time of day (inclusive).

stop_time

time (hh:mm:ss)

no

(always)

If specified, only match traffic before the given time of day (inclusive).

weekdays

list of weekdays

no

(always)

If specified, only match traffic during the given week days, e.g. sun mon thu fri to only match on sundays, mondays, thursdays and fridays. The list can be inverted by prefixing it with an exclamation mark, e.g. ! sat sun to always match but on saturdays and sundays.

monthdays

list of dates

no

(always)

If specified, only match traffic during the given days of the month, e.g. 2 5 30 to only match on every 2nd, 5th and 30rd day of the month. The list can be inverted by prefixing it with an exclamation mark, e.g. ! 31 to always match but on the 31st of the month.

The source address to use for NAT-reflected packets if reflection is 1. This can be internal or external, specifying which interface’s address to use. Applicable to DNAT targets.

limit

string

no

(none)

Maximum average matching rate; specified as a number, with an optional /second, /minute, /hour or /day suffix. Examples: 3/second, 3/sec or 3/s.

limit_burst

integer

no

5

Maximum initial number of packets to match, allowing a short-term average above limit

extra

string

no

(none)

Extra arguments to pass to iptables. Useful mainly to specify additional match options, such as -m policy --dir in for IPsec.

enabled

string

no

1 or yes

Enable the redirect rule or not.

On Attitude Adjustment, for NAT reflection to work, you must specify option dest lan in the redirect section (even though we're using a DNAT target).

Rules

Sections of the type rule can be used to define basic accept or reject rules to allow or restrict access to specific ports or hosts.

Up to Firewall v2, version 57 and below the rules behave like redirects and are tied to the given source zone and match incoming traffic occuring there.

In later versions the rules are defined as follows:

If src and dest are given, the rule matches forwarded traffic

If only src is given, the rule matches incoming traffic

If only dest is given, the rule matches outgoing traffic

If neither src nor dest are given, the rule defaults to an outgoing traffic rule

Port ranges are specified as start:stop, for instance 6666:6670. This is similar to the iptables syntax.

Valid options for this section are:

Name

Type

Required

Default

Description

src

zone name

yes ( optional since Firewall v2, version 58 and above)

(none)

Specifies the traffic source zone. Must refer to one of the defined zone names.

src_ip

ip address

no

(none)

Match incoming traffic from the specified source ip address

src_mac

mac address

no

(none)

Match incoming traffic from the specified mac address

src_port

port or range

no

(none)

Match incoming traffic from the specified source port or port range, if relevant proto is specified.

proto

protocol name or number

no

tcpudp

Match incoming traffic using the given protocol. Can be one of tcp, udp, tcpudp, udplite, icmp, esp, ah, sctp, or all or it can be a numeric value, representing one of these protocols or a different one. A protocol name from /etc/protocols is also allowed. The number 0 is equivalent to all.

dest

zone name

no

(none)

Specifies the traffic destination zone. Must refer to one of the defined zone names, or * for any zone. If specified, the rule applies to forwarded traffic; otherwise, it is treated as input rule.

dest_ip

ip address

no

(none)

Match incoming traffic directed to the specified destination ip address. With no dest zone, this is treated as an input rule!

dest_port

port or range

no

(none)

Match incoming traffic directed at the given destination port or port range, if relevant proto is specified.

ipset

string

no

(none)

If specified, match traffic against the given ipset. The match can be inverted by prefixing the value with an exclamation mark

mark

mark/mask

no

(none)

If specified, match traffic against the given firewall mark, e.g. 0xFF to match mark 255 or 0x0/0x1 to match any even mark value. The match can be inverted by prefixing the value with an exclamation mark, e.g. !0x10 to match all but mark #16.

start_date

date (yyyy-mm-dd)

no

(always)

If specifed, only match traffic after the given date (inclusive).

stop_date

date (yyyy-mm-dd)

no

(always)

If specified, only match traffic before the given date (inclusive).

start_time

time (hh:mm:ss)

no

(always)

If specified, only match traffic after the given time of day (inclusive).

stop_time

time (hh:mm:ss)

no

(always)

If specified, only match traffic before the given time of day (inclusive).

weekdays

list of weekdays

no

(always)

If specified, only match traffic during the given week days, e.g. sun mon thu fri to only match on sundays, mondays, thursdays and fridays. The list can be inverted by prefixing it with an exclamation mark, e.g. ! sat sun to always match but on saturdays and sundays.

monthdays

list of dates

no

(always)

If specified, only match traffic during the given days of the month, e.g. 2 5 30 to only match on every 2nd, 5th and 30rd day of the month. The list can be inverted by prefixing it with an exclamation mark, e.g. ! 31 to always match but on the 31st of the month.

Zeroes out the bits given by mask and ORs value into the packet mark. If mask is omitted, 0xFFFFFFFF is assumed

set_xmark

Zeroes out the bits given by mask and XORs value into the packet mark. If mask is omitted, 0xFFFFFFFF is assumed

family

string

no

any

Protocol family (ipv4, ipv6 or any) to generate iptables rules for.

limit

string

no

(none)

Maximum average matching rate; specified as a number, with an optional /second, /minute, /hour or /day suffix. Examples: 3/minute, 3/min or 3/m.

limit_burst

integer

no

5

Maximum initial number of packets to match, allowing a short-term average above limit

extra

string

no

(none)

Extra arguments to pass to iptables. Useful mainly to specify additional match options, such as -m policy --dir in for IPsec.

enabled

boolean

no

yes

Enable or disable rule.

Includes

It is possible to include custom firewall scripts by specifying one or more include sections in the firewall configuration.

There is only one possible parameter for includes:

Name

Type

Required

Default

Description

enabled

boolean

no

1

Allows to disable the corresponding include without having to delete the section

type

string

no

script

Specifies the type of the include, can be script for traditional shell script includes or restore for plain files in iptables-restore format

path

file name

yes

/etc/firewall.user

Specifies a shell script to execute on boot or firewall restarts

family

string

no

any

Specifies the address family (ipv4, ipv6 or any) for which the include is called

reload

boolean

no

0

Specifies whether the include should be called on reload - this is only needed if the include injects rules into internal chains

Includes of type script may contain arbitary commands, for example advanced iptables rules or tc commands required for traffic shaping.

Since custom iptables rules are meant to be more specific than the generic ones, you must make sure to use -I (insert) instead of -A (append) so that the rules appear before the default rules.

IP Sets

The UCI firewall version 3 supports referencing or creating ipsets to simplify matching of
huge address or port lists without the need for creating one rule per item to match,

The following options are defined for ipsets:

Name

Type

Required

Default

Description

enabled

boolean

no

1

Allows to disable the declaration fo the ipset without the need to delete the section.

external

string

no

(none)

If the external option is set to a name, the firewall will simply reference an already existing ipset pointed to by the name. If the external option is unset, the firewall will create the ipset on start and destroy it on stop.

name

string

yes if external is unset
no if external is set

(none) if external is unset
value of external if external is set

Specifies the firewall internal name of the ipset which is used to reference the set in rules or redirects.

family

string

no

ipv4

Protocol family (ipv4 or ipv6) to create ipset for. Only applicable to storage types hash and list, the bitmap type implies ipv4.

storage

string

no

varies

Specifies the storage method (bitmap, hash or list) used by the ipset, the default varies depending on the used datatypes (see match option below). In most cases the storage method can be automatically inferred from the datatype combination but in some cases multiple choices are possible (e.g. bitmap:ip vs. hash:ip).

match

list of direction/type tuples

yes

(none)

Specifies the matched data types (ip, port, mac, net or set) and their direction (src or dest). The direction is joined with the datatype by an underscore to form a tuple, e.g. src_port to match source ports or dest_net to match destination CIDR ranges.

iprange

IP range

yes for storage type bitmap with datatype ip

(none)

Specifies the IP range to cover, see ipset(8). Only applicable to the hash storage type.

portrange

Port range

yes for storage type bitmap with datatype port

(none)

Specifies the port range to cover, see ipset(8). Only applicable to the hash storage type.

netmask

integer

no

32

If specified, network addresses will be stored in the set instead of IP host addresses. Value must be between 1 and 32, see ipset(8). Only applicable to the bitmap storage type with match ip or the hash storage type with match ip.

maxelem

integer

no

65536

Limits the number of items that can be added to the set, only applicable to the hash and list storage types.

hashsize

integer

no

1024

Specifies the initial hash size of the set, only applicable to the hash storage type.

timeout

integer

no

0

Specifies the default timeout for entries added to the set. A value of 0 means no timeout.

Possible Storage / Match Combinations

The table below outlines the possible combinations of storage methods and matched datatypes as well as the usable IP address family.
The order of the datatype matches is significant.

Family

Storage

Match

Notes

ipv4

bitmap

ip

Requries iprange option

ipv4

bitmap

ip mac

Requires iprange option

ipv4

bitmap

port

Requires portrange option

any

hash

ip

-

any

hash

net

-

any

hash

ip port

-

any

hash

net port

-

any

hash

ip port ip

-

any

hash

ip port net

-

-

list

set

Meta type to create a set-of-sets

IPv6 notes

As described above, the option family is used for distinguishing between IPv4, IPv6 and both protocols. However the family is inferred automatically if IPv6 addresses are used, e.g.

Rules without IP addresses are automatically added to iptables and ip6tables, unless overridden by the family option.
Redirect rules (portforwards) are always IPv4 (for now) since there is no IPv6 DNAT support (yet).

Examples

Opening ports

The default configuration accepts all LAN traffic, but blocks all incoming WAN traffic on ports not currently used for connections or NAT. To open a port for a service, add a rule section:

Someone could ask "Ok, the packet source or destination is changed,
but still has to be forwarded towards the right network interface to reach the
endpoint". So the administrator of openwrt could wonder of adding
additional forwarding rules but no, it is not needed. The forwarding
rules are added by the firewall appliance itself.

The same applies to the masquerading, the rules are applied before
the global masquerading (if a masquerading is set), therefore they will
not be overridden (at least the SNAT) by the masquerading mechanism.

Masquerading on lan

Suppose that you have two routers, connected each other through the
lan zone (both have static ip and dhcp disabled),
and only one of them is connected to the internet through the wan zone.
In other words the situation is:

If both routers have the default openwrt configuration
(with the exceptions mentioned above), then a device on the lan side of the
router 1 can communicate through the internet if it has the router 1 as
gateway, this because the packet flow between devices is managed by routing.
In our case the router 2 has no proper setup in terms of gateway,
as the default openwrt configuration expects that a wan connection
on the router 2 is provided.

This rule is redirecting the tcp packets on the port 2023 with destination the wan ip of the router 1
(172.22.13.228) towards the lan ip of the router 2.
The router 2 cannot reply to those packets because we didn't adjust its routing table,
that is we didn't specify that the gateway to reply to "wan" sources is the router 1.
Indeed those redirected packets will have an source ip external from the (default) "lan" zone 192.168.1.0/24.

We can solve this activating the masquerading on the "lan" zone on the router 1, in this way.

This setup will provide the following effect (that is the effect intended by the masquerading): if a packet, belonging to a certain connection, is coming into the lan zone with a source ip belonging to another zone, keep track of the connection, taking note of the source ip of that connection, and modify the source ip with the ip of the router in the lan zone (that is: source_ip from a.b.c.d to 192.168.1.254).
Then deliver the packet to the intended destination (that is, 192.168.1.1, the router2). Afterwards, if a packet from 192.168.1.1 is coming back towards 192.168.1.254, belonging to the connection tracked before, changed back the destination ip (here is the second effect of the masquerading) with the source ip memorized before (that is, dest_ip from 192.168.1.254 to a.b.c.d ). In this way, for the point of view of the router 2, the router 2 just communicate with a device with an ip belonging to its "lan" zone , and therefore the default routing is working without problem.

At least one side effect of this setup is that every device in the lan zone of the router 1 cannot see any "wan" ip, and this could be not wanted for several reasons (one of which: if you setup a proper gateway, there is no need for this masquerading). But this was just a "special case" to expose in brief how the masquerading works and how it could be applied to zones that usually don't use it. An improvement of "masquerading only for a specific device in the zone" could be the following:

When used alone, Source NAT is used to restrict a computer's access to the internet, but allow it to access a few services by forwarding what appear to be a few local services, e.g. NTP, to the internet. While DNAT hides the local network from the internet, SNAT hides the internet from the local network.

Source NAT and destination NAT are combined and used dynamically in IP masquerading to make computers with private (192.168.x.x, etc.) IP address appear on the internet with the OpenWrt router's public WAN ip address.

True destination port forwarding

Most users won't want this. Its usage is similar to SNAT, but as the the destination IP address isn't changed, machines on the destination network need to be aware that they'll receive and answer requests from a public IP address that isn't necessarily theirs. Port forwarding in this fashion is typically used for load balancing.

Transparent proxy rule (external)

The following rule redirects all outgoing HTTP traffic from lan through an external proxy at 192.168.1.100 listening on port 3128.
It assumes the OpenWrt lan address to be 192.168.1.1 - this is needed to masquerade redirected traffic towards the proxy.

Then create the zone in /etc/config/firewall, for example one zone for all the vpn interfaces.

config zone
option name vpn_tunnel
list network 'tun0'
list network 'tun1'
option input ACCEPT
#the traffic towards the router from the interface will be accepted
#(as for the lan communications)
option output ACCEPT
#the traffic from the router to the interface will be accepted
option forward REJECT
#traffic from this zone to other zones is normally rejected

Then we want to communicate with the "lan" zone, therefore we need forwardings in both ways
(from lan to wan and viceversa)

This will create a lot of "automatic" iptables rules (because automatic scripting is not
as efficient as raw iptable commands in /etc/firewall.user)
but those rules will be more clear in the luci webinterface and also more readable for
less expert users.

In general remember that forwardings are relying how routing rules are defined, and afterwards which zones are
defined on which interfaces.

Zone declaration for non-UCI interfaces

This example declares a zone which maches any Linux network device whose name begins with "ppp".

Forwarding IPv6 tunnel traffic

This example is for IPv6 tunnels only, and does not apply to native dual-stack interfaces.

Unverified Information!
From my experience all you need to do is just add the interface name of your ipv6 tunnel to the wan zone of your firewall. This worked for me Remove the information below if this is the correct way to proceed.

Caveat: The above will only work if the tunnel is bringing IPv6 connectivity to the router itself. If you use the tunnel to route a prefix into your lan as well, you will additionally need to allow Inter-Zone Forwarding from wan to lan (not enabled by default). Creating a separate firewall zone (as described below) is a cleaner solution, though.

IPv6 packets are by default not forwarded from lan to your wan6 interface and vice versa. Make sure to add net.ipv6.conf.all.forwarding=1 in /etc/sysctl.conf to enable it permanently. Assuming your tunnel interface is called henet, add the following sections to /etc/config/firewall to create a new zone wan6, covering henet and allowing forwarding betweeen wan6 and lan in both directions:

The family option ensures that the zone and all associated entries (rule, forwarding and redirect sections) are only added to ip6tables but not iptables.

Manual iptables rules

Traditional iptables rules, in the standard iptables unix command form, can be specified in an external file and included in the firewall config file. It is possible to include multiple files this way.

The syntax for the includes is Linux standard, and therefore different from UCI's; its documentation can be found in netfilter.

Firewall management

After a configuration change, firewall rules are rebuilt by executing /etc/init.d/firewall restart; calling /etc/init.d/firewall stop will flush all rules and set the policies to ACCEPT on all standard chains.
To manually start the firewall, call /etc/init.d/firewall start.

The firewall can be permananently disabled by executing /etc/init.d/firewall disable.
Note that disable does not flush the rules, so it might be required to issue a stop before.
Use enable to activate the firewall again.

Temporarily disable firewall

Run /etc/init.d/firewall stop to flush all rules and set the policies to ACCEPT.
To restart the firewall, run /etc/init.d/firewall start.

Hotplug hooks (8.09.2+)

In addition to includes it is possible to let the firewall execute hotplug handlers when interfaces are added to a zone or removed from it. This is useful to create rules for interfaces with dynamic ip configurations (dhcp, pppoe) on the fly.

Each time an interface is added or removed from a zone, all scripts in the /etc/hotplug.d/firewall/ directory are executed. Scripts must be named in the form NN-name with NN being a numeric index between 00 and 99. The name can be freely choosen.

Once a handler script is invoked, the information about the event is passed through the environment.
The table below lists defined variables and their meaning.

Variable

Description

ACTION

Type of the event: add if an interface was added, remove if it was removed

ZONE

Name of the firewall zone the interface was added to

INTERFACE

OpenWrt name of the interface, for example "lan" or "wan" - corresponds to the interfaces defined in /etc/config/network

DEVICE

The physical interface involved, for example "eth0" or "ppp0"

Implications of DROP vs. REJECT

The decision whether to drop or to reject traffic should be done on a case-by-case basis. Many people see dropping traffic as a security advantage over rejecting it because it exposes less information to a hypothetical attacker.
While dropping slightly increases security, it can also complicate the debugging of network issues or cause unwanted side-effects on client programs.

If traffic is rejected, the router will respond with an ICMP error message ("destination port unreachable") causing the connection attempt to fail immediately. This also means that for each connection attempt a certain amount of response traffic is generated. This can cause harm if the firewall is "attacked" with many simultaneous connection attempts; the resulting "backfire" of ICMP responses can clog up all available bandwidth and make the connection unusable (DoS).

When connection attempts are dropped the client is not aware of the blocking and will continue to re-transmit its packets until the connection eventually times out. Depending on the way the client software is implemented, this could result in frozen or hanging programs that need to wait until a timeout occurs before they're able to continue.

Also there is an interesting article which that claims dropping connections doesnt make you any safer - Drop versus Reject.

DROP

less information is exposed

less attack surface

client software may not cope well with it (hangs until connection times out)

may complicate network debugging (where was traffic dropped and why)

REJECT

may expose information (like the ip at which traffic was actually blocked)

Notes on connection tracking

NOTRACK

By default, the firewall will disable connection tracking for a zone if no masquerading is enabled. This is achieved by generating NOTRACK firewall rules matching all traffic passing via interfaces referenced by the firewall zone. The purpose of NOTRACK is to speed up routing and save memory by circumventing resource intensive connection tracking in cases where it is not needed. You can check if connection tracking is disabled by issuing iptables -t raw -vnL, it will list all rules, check for NOTRACK target.

NOTRACK will render certain ipables extensions unusable, for example the MASQUERADE target or the state match will not work!

If connection tracking is required, for example by custom rules in /etc/firewall.user, the conntrack option must be enabled in the corresponding zone to disable NOTRACK. It should appear as option 'conntrack' '1' in the right zone in /etc/config/firewall.
For further information see http://security.maruhn.com/iptables-tutorial/x4772.html .

nf_conntrack_skip_filter

Since r42048, there is a new setting activated by default which causes the packets with the established state, completely bypass iptables filter table. This is to help with network performance and unless you need all packets to be counted by iptables filter or have some specific rules which would apply to already established connections, you should leave it active.

This behavior can be disabled by editing /etc/sysctl.conf :

net.netfilter.nf_conntrack_skip_filter=0

and then activating the new setting:

sysctl -p

or be temporarily turned off untill the next reboot by issuing :

sysctl -w net.netfilter.nf_conntrack_skip_filter=0

How to delete a rule

If you made a mistake you can delete a rule this way.

First, issue this command to find the index of the rule:

# iptables -L -t raw --line-numbers

Now to delete, e.g. the third rule from chain OUTPUT, execute:

# iptables -t raw -D OUTPUT 3

Debug generated rule set

It is possible to observe the iptables commands generated by the firewall program,
this is useful to track down iptables errors during firewall restarts or to verify
the outcome of certain uci rules.

In order to see the rules as they're executed, run the fw command with the FW_TRACE
environment variable set to 1 (one):

# FW_TRACE=1 fw reload

To direct the output to a file for later inspection, use the command below:

# FW_TRACE=1 fw reload 2>/tmp/iptables.log

If you are using the firewall3, you can enable debug mode using the -d switch:

# fw3 -d reload 2>/tmp/iptables.log

Furthermore it is also possible to print the to-be generated ruleset using the print command in conjunction with the -4 and -6 switches: